1. Field of the Invention
This invention relates to an information reproducing apparatus for detecting a reproducing position on a disk on which information has been recorded at a constant linear velocity.
2. Prior Art
Information reproducing apparatuses for optically reproducing information from a recording medium such as video disk or optical disk have been widely used. In these information reproducing apparatuses, particularly in the constant linear velocity (CLV) disk drive apparatus, a again in a motor control circuit is changed according to the reproducing position on the disk, since the number of rotations of the disk varies according to a radius position of the disk.
The principle of detecting the reproducing position on a disk as mentioned above, is described in Japanese unexamined patent application publication No. 55-139641, which is described below with reference to FIG. 17.
FIG. 17 shows the principle of detecting the reproducing position of the conventional information reproducing apparatus by use of a potentiometer. A disk 801 set on a turn table 802, which is fixed to a shaft of a motor 803, is turned by driving the motor 803. An information signal recorded on the disk 801 is reproduced by focusing a light flux 811 on the information recorded surface of the disk 801 and driving a pick-up 804 in the x-direction.
A brush 805 fixed in the pick-up 804 moves to the x-direction while keeping in contact with a resistor 806. Accordingly, a voltage, which is realized by dividing a voltage Vcc with resistors R1 and R2, is generated at the brush 805, the voltage being varied with movement of the contact of the brush 805 with the resistor 806. The brush voltage 807 is compared with a reference voltage 808 by a comparator 809 in order to find the present disk reproducing position. The gain in the motor control circuit is switched in accordance with the result thus obtained.
However, with the above mentioned arrangement, the reproducing position of the disk can not be detected in some cases due to poor contact of the brush with the resistor, and further there is the structural limitation of mounting the potentiometer.